Nylon-MXD6 is a generally used plastic for obtaining a good gas barrier against oxygen and CO2. In this respect, nylon-MXD6 is used as a barrier layer in PET preforms.
A first problem with nylon-MXD6 lies in its clarity or transparency, in the sense that this material loses its transparency when it absorbs water. This transparency is necessary however for a large number of applications, such as in preforms or containers on which flawless transparency requirements are frequently imposed. This loss of transparency is a first drawback of nylon-MXD6.
A further problem is with the adhesion properties, which are insufficient in the case of nylon-MXD6, which are even such that nylon-MXD6 cannot be used as a barrier material in preforms having polyolefins such as polyethylene and polypropylene as the primary base material, because of this adhesion problem of a barrier layer made of nylon-MXD6 vis-a-vis polyolefins. This limitation on material choice is an additional drawback of nylon-MXD6.
The known nylon-MXD6 also exhibits poor adhesion to PET. This means thus a limited use of PET as a primary base material, with an adverse consequence in terms of design freedom and container design.
A still additional problem is that nylon-MXD6 causes severe corrosion on the metal surfaces of injection moulding machines and moulds used in the injection moulding of preforms or other hollow articles. This corrosion results in high maintenance costs, since it causes the need to replace certain machines and mould parts.
Since nylon-MXD6 thus has certain drawbacks, alternatives lacking these drawbacks are being sought for a long time. These notably include other plastic materials consisting of meta-xylene-based polymers, having good gas barrier properties just like those of nylon-MXD6, but without the aforementioned drawbacks of nylon-MXD6.
Various patent publications disclose the structure of nylon-MXD6, as well as the good gas barrier that this forms, namely barriers exclusively against gases but no other components. However, this constitutes a limitation on this known material, because this means that such barriers cannot efficiently be used against other phases, notably water vapour, fluid etc.